Polyimide hollow spheres

ABSTRACT

A method of making polyimide hollow spheres from a tetracarboxylic acid-ditertiary amine reaction product and an aromatic diamine in an aqueous solution.

United States Patent Glenn R. Wilson Dayton, Ohio Nov. 9, 1967 Dec. 7,197 l Monsanto Research Corporation St. Louis, Mo.

Inventor App]. No. Filed Patented Assignee POLYIMIDE HOLLOW SPHERES 6Claims, No Drawings U.S. Cl 260/2.5 B, 260/2.5 N, 260/2.5 D, 260/47 CZ,260/65, 260/78 TF, 260/857, 260/858, 260/859 Int. Cl BOlj 13/02, C08j1/14 Field of Search 260/2.5 N, 2.5 B

[56] References Cited UNlTED STATES PATENTS 2,797,201 6/1957 Veatch eta1 260/2.5 B 3,249,56l 5/1966 Hendrix 260/2.5 N 3,256,219 6/1966 Will260/2.5 N 3,287,311 11/1966 Edwards... 260/2.5 N 3,310,506 3/1967Amborski et a1. 260/2.5 N 3,440,197 4/1969 Boldebuck et a1. 260/29.23,172,867 3/1965 Showalter 260/2.5 B 3,293,114 12/1966 Kenaga et al.260/2.5 B

Primary Examiner-Murray Tillman Assistant ExaminerMorton F oelakAttorney-L. Bruce Stevens, .lr.

ABSTRACT: A method of making polyimide hollow spheres from atetracarboxylic acid-ditertiary amine reaction product and an aromaticdiamine in an aqueous solution.

POLYIMIDE HOLLOW SPHERES The invention described herein was made in thecourse of, or under, a contract with the U.S. Atomic Energy Commission.

CROSS-REFERENCE TO RELATED APPLICATIONS The polyimide-forming reactionmixture used herein is disclosed in application Ser. No. 681,93 l, filedof even date.

BACKGROUND OF THE INVENTION According to the invention, there isprovided a new and valuable method for preparing polyimide hollowspheres. Polyimide compositions are generally well-known in the art. Seee.g., U.S. Pat. Nos. 3,249,561, issued May 3, 1966 to E. I. duPont deNemours and Company, and 2,867,609, issued Jan.

6, 1959 to E. I. duPont de Nemours and Company. They are usuallyprepared by reaction of an aromatic tetracarboxylic acid dianhydridewith an organic diamine to obtain an intermediate, curable prepolymerwherein there are present amide linkages from an amino group of thediamine and a carboxy group of the tetracarboxylic component, and twocarboxy groups of the tetracarboxylic component which have not reactedwith the organic amine component. Upon heating, cyclization occurs byreaction of the unreacted carboxylic group at the amide portion of thepolymer to give an imide structure. Thus, condensation of, say, l,2,4,5-benzenetetracarboxylic dianhydride and p-phenylene-diamine to give aprepolymer amide-acid and curing of the latter to a polyimide proceedssubstantially as follows:

0 O H II C C\ 0 /o nmQan-r, t

\C C II ll 0 O H O O H r u g l 41,0

HOC (|?OH 0 O I] II H ll where n denotes the degree of polymerization.

Because curing of the polyamide/acid gives the exceptionally stablepolyimides, the prepolymers are of great potential interest for thepreparation of heatand solvent-resistant compositions. In suchapplications, curable materials are generally most expediently employedin solution. However, the usual prior art polyamide/acids possesslimited solubility; hence, in order to employ them in these fields, ithas been necessary to use such uncommon, expensive solvents as N-methylpyrrolidinone, dimethylformamide, dimethyl acetamide, dimethylsulfoxide, etc. A further limitation of the wide applicability of thepolyamide/acids is the noxious nature of 5 such solvents.

The present invention overcomes these and other problems.

SUMMARY HOzC COzH wherein R represents a tetravalent radical selectedfrom the group consisting of zzx w Oi) it I with approximately two molesof a tertiary amine having a base strength (K in water) of 1X10 to lXlOand having a boiling point below 200 C. together with a diamine of theformula H NZNI-I wherein Z is an aromatic hydrocarbon radical havingfrom six to 18 carbon atoms, said diamine having at least one carbonatom between each amino group and being present in the amount ofapproximately one mole for each mole of the tetracarboxylicacid-ditertiary amine reaction product, and water in the amount of 20 to60 percent by weight of the said reaction mixture, concentration of saidreaction mixture under vacuum to obtain a loosely divided solidintermediate product, sparsely distributing the intermediate solidproduct thus obtained into various uniform sizes, and further heatingthe intermediate product from l20 to C. for 1 minute to 1 hour to obtaincurable hollow spheres.

The improvement of the invention over the older methods of preparingpolyimide compositions lies in the use of water as a solvent for thepolyimide-forming reaction mixture. This is accomplished by forming thereaction product of a tetracarboxylic acid in an aqueous solution usinga tertiary amine. After solution of the acid-amine reaction product hasbeen achieved, an aromatic primary diamine is added to the solution. Thepolyimide-forming reaction mixture may then be stored at roomtemperature or lower for an indefinite period of time, or polymerizationmay be presently effected to produce curable hollow spheres ashereinbefore described.

Although the mechanism by which polymerization takes place is not fullyknown, it is believed that upon heating, the acid-amine reaction productundergoes a change to the dianhydride and, upon further heating, thedianhydride reacts with the primary diamine to form the polyimide. Thus,condensation of, say, the dipyridinium reaction product of l,2,4,5-benzenetetracarboxylic acid in water and m-phenylenediamine to give thetetracarboxylic dianhydride and curing of the latter with the diamine toa polyimide proceeds substantially as follows:

(I) benzophenonetetracarboxylic acid; bis(3,4-dicarboxylicpheno oyl)methane; l,2-bis(3,4-dicarboxylicphenyl)ethane; 1,1- e g eqa heatbis(3,4-dicarboxylicphenyl)ethane; 2,2-bis(3,4-dicarboxyl- H2Oicphenyl)propane; l,l-bis(3,4-dicarboxylicphenyl) propane;,

bis(3,4-dicarboxylicphenyl)ether; bis(3,4-dicarboxy1icphen- 11yl)sulfide; bis(3,4edicarboxylicphenyl)sulfone; 3,3',4,4- O 0biphenyltetracarboxylic acid; 2,3,6,7-naphthalenetetracar-- boxylicacid; 1,2,5,6-naphthalenetetracarboxylic acid; J C N1,4,5,8-naphthalenetetracarboxylic acid, etc. The dian- 1o hydrides ofthe tetracarboxylic acids may also be employed, 0 O 2 for when thedianhydride is added to the water, and the mix- \C ture heated, thetetracarboxylic acid is formed.

ll Any aromatic primary diamine having six to 18 carbon atoms may beused, provided that their is at least one carbon h atom between theamino groups.

C 0 Examples of such diamines are: m-phenylenediamine; P- ii heatphenylenediamine; 2,7-naphthalenediamine; 3,6- 0 naphthalenediamine;bis(3-aminophenyl)methane; bis(4- aminophenyl)butane;2,7-anthracenedianmine; 3,6- anthracenediamine;p-terphenyl-4,4"'-diamine; p-terphenyl- 0 A 5,3"-diamine, etc.

0 in order to achieve solution of the tetracarboxylic acid in water(i.e. as the acid-amine reaction product), it is necessary that there bepresent 2 moles of the tertiary amine for every 21120 mole of the acid.Although this amount of the tertiary amine reacts with only 2 of the 4carboxy groups, it has been found that this ratio of amine to acid issufficient to completely disg H solve the acid so long as the totalcomposition contains O h between 20 to 60 percent by weight water.

The reaction product of the tetracarboxylic acid and the wherendehotesthe degree ofpelyfhehzahoh tertiary amine and the aromatic primarydiamine are ad- The hbseheeof Polyarme e In the final eompesmehvantageously employed in equal stoichiometric proportions, deten'h'hedby 'hh' absorphoh P The Sheena of the i.e., one mole of the acid-aminereaction product per mole of present compositions are characterized byabsorption at 5 the diamine. However, a slight excess of eithercomponent microns, indicating an imide linkage, and at 5.8 microns duemay be used to e C 0 bond of the earbexyl groups- The absence ofThepresently provided polyimide hollow spheres may be; sorPhoh band?represehhhg and C bonds of the used in a wide variety of applications.The curable hollow amide groups indicates full conversion of thereactants to the spheres are formed by heating under a vacuum at atemper? poiy'mlde polymeh ture not to exceed 1 10 C. preferably about 90C. for a period The preferred tertiary amines have a boiling point belowof 1 to 10 hams7 and preferably about 8 hours, an aqueous 200 so P theymay be from the mixture of a tetracarboxylic acid (or its dianhydride)tertiaryreaction mixture before polymerization is completed. The aminereaction product and a primary aromatic diamine base strength (K,, inwater) of the tertiary amines used herein There is obtained a fluff ysolid. In order that this solid may hes m the range i lxlo- 3 lxlo Ifthe bese Str-ength ls be evenly separated a sieve or ah othehsuitablemeans ma I greater than IX 10 the ionic strength of the acid-amine reacyy tion product may be such as to prevent formation of the diane employedto e e the Solid into partielee various hydride from the acid atmoderate temperatures Conversely, uniform sizes. The particles are thensparsely distributed over, if the base strength is less than l l0, thetertiary amine will I examPlei a Mn-mated These WW1es f not be strongenough to react with the acid, and therefore mbuted m such a manner thattheyoare not ouehmg P solution of the acid in water cannot be achieved.38 0! the e They are heated at for a useful tertiary amines, togetherwith their base strengths (K,, in suffie'em to form the hollow p -8 1hour and water at C) and boiling points trimethylamine preferably about15 to 20 minutes. The curable hollow (5.5X10, 4 C.); triethylamine (5.7l0" 90 (2.); spheres thus obtained are rather delicate, forpolymerization is tripropylamine. (4'4X10 1560 C); triisobutylamine notcomplete, and the spherical structure is still permeated (2 6 10-,methyldiethylamine (2'7x10-. with solvent unpolymerized reactants. Thesespheres may be dimethylethylamine dimethyp fully cured by heating toabout 350 C. for 3 hours, and propylamine 0- 5 dimethylbutylaminepreferably 1 to 2 hours. Or the curable hollow spheres may be 1 1 1 9495 dimethylisobutylamine 2 1 placed in a mold and heated (not to exceed350 C.) and pres- 31 Q); mb ldi h l i (4 1 1 89 9() C 60 sure of to 300psi. maybe applied to obtain an essentially methyldiisopropylamine 1 110- 109 112 Q 1 2. rigid integral structure consisting of fused hollowspheres. The bis(dimethylamino)ethane (9X10', C.); l,2- thus obtainedstructure is flameproof and highly resistant tobis(dimethylamino)propane (3x10 -l40 C.); 13- heat; hence, it isparticularly valuable as an insulating materibis(dimethylamino)butane1X10", Py n al. The toughness and heat-stability of these'structuresrecom- (2.3X10', 1 15 C.); 2-methylpyridine (1.5Xl0" 128 C.); 3- 65 mendthem for use in any application where a combination of methylpyridine(4.8Xl0'- 144 C.); 4-methylpyridine these properties is desired,'e.g.,fire walls in automotive vehi- (l.l l0', 143 C.); 2,4-dimethylpyridine(5.2 10'- 157 cles, furnace insulation, roof, wall, and ceilinginsulation, C.); 2,6-dimethylpyridine (4.9X10'- 143 C.); 3,4-dimethyl-Steam pip e cpyridine (3.3 l0" 163 C.); 2-ethylpyridine (9.7 l0'- 70 Thecurable hollow spheres or the fully cured hollow C.); 4-ethylpyridine(1.1X10'- 166 C.); Z-methyI-S-ethylspheres may be employed in otherpolymers, e.g., polystyrene, pyridine (3.2Xl0'- 174 C.);dimethylaminoethanol polyethylene, polypropylene, polyurethane,polyamides, etc.,

( l .4 l0, 135 C.); diethylaminoethanol (5X 10*, 163 C.); to preparesyndiotactic foams. diisopropylaminoethanol (8.2Xl0" l87'l 92 C.), etc.Accordingly, an object of this invention is the provision of Examples ofuseful acids are: l,2,4,5-benzenetetracarboxylimproved startingmaterials for the preparation of polyimide ic acid; 3324,41biphgyltetracarbgxyhg agd, 3,31,51,4 hollow spheres. Another object isthe provision of water as the solvent for the polyimide-forming reactionmixture. A most important object is the provision of new polyimidehollow. spheres.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention is furtherillustrated by, but not limited to the following examples:

EXAMPLE I A mixture of 644.4 g. (2 moles) of 3,3',4,4'-benzophenonetetracarboxylic acid dianhydride and 795.2 g. water was thoroughly mixedto form a suspension. Over a period of minutes 332.2 g. (4.2 moles) ofpyridine was added, with a resulting temperature rise to 68 C. Afterletting the mixture cool to room temperature 216.2 g. (2 moles) ofm-phenylene diamine was rapidly added without an increase in temperatureand the solution was then stirred for 1 hour. This solution was storedat room temperature for about 1 week.

The solution was then concentrated under a vacuum at 90 C. forapproximately 8 hours to yield a flufi'y solid residue containing 27percent volatiles (as shown by percent weight loss of a sample afterheating for 3 minutes at 315 C.). The flufi'y solid was screened througha mesh-sieve and sparsely distributed over the surface of ateflon-coated pan. The tray was then heated at 125 to 135 C. for 15minutes under vacuum during which time the particles were converted tohollow spheres ranging in size from 0.02 mm. to 0.5 mm. (volatilecontent approximately 21 percent). The spheres were screened to variousuniform sizes and the wall strength was increased by curing at 3 15 C.

EXAMPLE 11 After conversion to the curable hollow spheres by heating at125 to 135 C. as described in example I, the spheres are placed in amold and the mold is heated to 300 C. at a pressure of 150 p.s.i. for 45minutes. Thereis obtaineda wellfused integral structure.

EXAMPLE Ill A polyimide-forming reaction mixture is prepared asdescribed in example I except that 700 g. (2 moles) o f3,3',4,4'3,3',4,4'ficient water (826.6 g.) is used to achieve a solutionhaving 60'percent solids.

After heating under a vacuum at 90 C. for approximately 8 hours,screening through a 20 mesh sieve, and heating on a Teflon-coated pan at125 to 135 C. as in example I, there is obtained hollow spheres rangingin size from 0.02 mm. to 0.5 mm. The spheres are screened'to variousuniform sizes and made stronger by curing at 315 C.

EXAMPLE 1V After conversion to the curable hollow spheres by heating at125 to 135 C. as described in example III, the spheres are placed in amold and the mold is heated to 300 C. at a pressure of 150 psi. for 45minutes. There is obtained a wellfused integral structure which isheat-resistant and flameproof.

It is to be understood that although the invention has been describedwith specific references to particular embodiments thereof, it is not tobe so limited since changes and alternations therein may be made whichare within the full intended scope of this invention as defined by theappended claims.

What I claim is:

1. A method for making curable hollow spheres which comprises A. heatingunder a vacuum at a temperature below 110 C.

for l to 10 hours a polyimide-forming reaction mixture consisting of a.the reaction product consisting essentially of the product obtained byreacting approximately one mole of a tetracarboxylic acid of the formulav l HOgC COzH H020 COzH wherein R represents a tetravalent radicalselected from the group consisting of with approximately two moles of atertiary amine having a base strength (K,, in water) of 1X10" to 1X10and a boiling point below 200 C. together with b. a diamine of theformula H,NZNI-l wherein Z is an aromatic hydrocarbon radical havingfrom six to 18 carbon atoms, said diamine having at least one carbonatom between each amino group and being present in the amount ofapproximately one mole for each mole of the tetracarboxylic acidditertiary amine reaction product, and

c. water in the amount of 20 to 60 percent by weight of the saidreaction mixture, that is concentrated under vacuum to obtain a looselydivided solid intermediate product,

B. separating said solid intermediate sizes, 7

C. sparsely distributing the uniformly sized product obtained in step 8on a suitable surface,

D. further heating the intermediate product from to C. for 1 minute to 1hour to obtain curable hollow spheres.

2. The method defined in claim 1 wherein the diameter of the curablehollow spheres is from 0.01 mm. to 1.0 mm.

3. The method defined in claim 1 wherein the curable hollow spheres arefurther headed to about 350 C. to obtain fully cured hollow spheres.

m 4. The method defined in claim 1 wherein R is 5. The method defined inclaim 1 wherein Z is phenylene. .6.- The m h s fin i im lat he n R is.

product into uniform and Z is phenylene.

UNITED STATES PATENT OFFICE vGERTIFI(IiTE OF C O RRECTEON atenm,3,625,873 D e December 7, 1971 Inventor(s) Glenn R. Wilson- It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:v

Column 6, between-1 lines 14 and-l5, add the following:

@eeo @QHQ 9 line SQQchan gef"headed" to heated lines 42-59, cancel theentire contents of this line and insert in place thereof lines 6 974,cancel Signed and sealed this 24th day of December 1974.

(SEAL) Attest: I v

McCOY M. GIBSON JR. G. MARSHALL DANN Attesting Officer Commissioner ofPatents FORM PO-1050 (10-69) uscoMM-Dc 60376-P69 US. GOVERNMENT PRINTINGOFFICE I969 0-566-384,

2. The method defined in claim 1 wherein the diameter of the curable hollow spheres is from 0.01 mm. to 1.0 mm.
 3. The method defined in claim 1 wherein the curable hollow spheres are further headed to about 350* C. to obtain fully cured hollow spheres.
 4. The method defined in claim 1 wherein R is
 5. The method defined in claim 1 wherein Z is phenylene.
 6. The method as defined in claim 1 wherein R is 